Screw-rotor compressors or motors



Dec. 13, 1960 J. R. MUNCK AF ROSENSCHLD ETAL SCREW-ROTOR COMPRESSORS ORMOTORS Filed .Aprill 16. 1958 Fig. 2

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3 Sheets-Sheet l Dec. 13, 1960 2,963,884

J. R. MUNcK AF Rosx-:NscHLD ET AL SCREW-ROTOR COMPRESSORS OR MOTORSFiled April 16. 1958 3 3 Sheets-Sheet 2 6 Fig. [+V 2O Illa.' Y i/\f////// /f/ f 7 Ill HNI

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Dec. 13, 1960 2,963,884

J. R. MUNCK AF RosENscHLD ETA.

SCREW-ROTOR COMPRESSORS OR MOTORS Filed April 16, 1958 3 SheeS-Shee'l'l3 ATTORNEY SCREW-KOTOR COMPRESSRS R MOTORS John Rutger Munck afRosenschld, Saltsjobaden, and Sven Ivar Trulsson, Nacka, Sweden,assignors to Atlas sCopco Aktiebolag, Nacka, Sweden, a corporation ofweden Filed Apr. 16, 1958, Ser. No. 728,861 Claims priority, applicationSweden Apr. 17, 1957 3 Claims. (Cl. 62-331) This invention relates toscrew-rotor compressors or motors operating on an elastic working fluidand comprising a casing and two or more screw-type rotors mounted inbearings in said casing and intermeshing to form working chambers forsaid working uid which working chambers move from registry with an inletport at the casing in which one uid pressure prevails to register withan outlet port at the casing in which another uid pressure prevails, asthe rotors revolve. Machines of the above type are most commonly used ascompressors but may also be operated as motors. For the sake ofsimplicity, the following etailed description of apparatus embodying theinvention describes such apparatus only when used as a compressor, whichfact, however, should not be considered as a limitation of the scope ofthe invention as set forth in the claims.

.aired States Patent In apparatus of the kind under consideration, forsmall pressure differences, i.e. less than 2 kilogrammes per squareeentimetre, it has been possible to use ball bearings for the mountingof the rotor shafts and it has also been possible to arrange the rotorsin the casing in any convenient manner. In such compressors operatingwith a pressure difference in excess of 2 kgs./sq.cm. between the inletand the outlet of the compressor it has been common practice to use onlyplain bearings for the rotor shafts since the bearing loads have beenconsidered too high for ball or roller bearings at the speeds at whichsaid compressors are normally operated. Compressors of the kind underconsideration have the disadvantage that they produce an intense andirritating noise. Such compressors have, further, the disadvantage thatthe ediciency drops very quickly if the clearance between the rotors andbetween the rotors and the casing is larger than absolutely necessary.One object of this invention is to reduce the above mentioneddeficiencies and to provide a compressor which emits as littledisturbing noise as possible in the room Iwhere the compressor ismounted and which simultaneously shows a good eciency and has smallbearing loads.

By locating the rotor shafts in a common horizontal plane with the portcommunicating with the working chambers in which the high pressureprevails disposed at the underside of the rotors and with the portcommunicating with the working chambers in which the low pressureprevails disposed at the upper side of the rotors the pressuredifference between the upper and the under sides thereof duringoperation `of the compressor or motor helps to lift the rotors and theweight of the rotors is consequently partially compensated for, so thata portion of the radial pressure on the radial bearings of the rotorshafts is counterbalanced by fluid pressure. The provision of radialroller bearings for the rotor shafts makes it possible to reduce theclearance between the rotors and between the rotors and the casing to aveiy small value so that leakage through the machine is reduced to aminimum and the eihciency is increased which is also a result of thereduced bearing loads and of the reduction of the frictional resistanceproduced thereby.

2,953,884 Patented Dec. 13, 196() are The invention has, furthermore,the advantage that the casing enclosing the rotors may be dividedhorizontally along the common rotor shaft plane so that the upper half`of the casing may be `removed for inspection without moving other partsof the machine or of the pipe connections. The provision ofnoise-emitting pipes and conduits below the door of the room in whichthe compressor or motor is mounted reduces the disturbing noise in saidroom materially so that the noise in said room is on an acceptable leveland, furthermore, the forces originating from the system of pipes andconduits is transmitted directly to the foundation of the compressor ormotor without stressing the compressor or motor casing. By providing theopening in which the high pressure prevails at the underside of thecasing, said casing may without inconvenience be provided withstiffening ribs or the like at the portion which has the greatest load.Conduits to an intermediate cooler of a compressor which may preferablybe disposed below the door level may in accordance with the invention bemade with reduced length which also helps to maintain good ediciency andto lreduce the disturbing noise.

The above and other `detailed objects of the invention and theadvantages to be derived from its use will appear as the ensuing portionof this specification proceeds.

In the accompanying drawings one embodiment of a compressor plant and ascrew compressor embodying the invention is illustrated by way ofexample.

Fig. l isa side view and partial section of a compressor plant embodyingthe invention. Fig. 2 is an end view of the plant according to Fig. l.Fig. 3 is a longitudinal section through yone of the screw compressorsshown in Figs. l and 2. Fig. 4 is a plan View of the compressor shown inFig. 3. Fig. 5 is a section yon line V-V in Fig. 3, and Fig. 6 is asection on line VI--V I in Fig. 3.

The compressor plant illustrated in Figs. l and 2 consists of alow-pressure compressor 1, a high-pressure compressor 2 and an electricmotor 3 which drives the compressors. The motor and the compressors aremounted in a machine room on a concrete foundation 4. The compressors 1and 2 are essentially of the same design and in order to disclose theinvention the high pressure compressor 2 only is described in detail.Said compressor consists of a casing which comprises a lower portion 5and an upper portion 6 providing two horizontally extending intersectingbores for the reception of the rotors, a two-piece intake end closurestructure 7, S, and an end closure structure 9 at the outlet end. Air issupplied to the compressor '2 through a conduit 10 which at the opening11 is connected to the underside of the casing portion 7, S, and the aircompressed in the compress-or 2 is discharged from the compressorthrough a pipe 12 which at the opening 13 is connected to the undersideof the compressor casing portion 5. In the compressor casing twoscrew-type rotors 14 and 15 are mounted with their shafts in radialIroller bearings 16 and 17, respec tively, with the shafts disposed in asingle horizontal plane 31. The rotors are, furthermore, provided withplain thrust bearings 13 at one end to take care of the axial forces.From the opening 11 the passage 19 in the inlet end closure structure 7,8 leads to an inlet port 2G at one end of the upper end portion of thebores in which the rotors are situated and from an outlet port 21 at thelower end portion of the bores in which the rotors are situated apassage 22 runs from the underside of the rotors to the pipe 12 andfurther through an aftercooler 23 to a pipe line 24. From the drawingsit will be evident that the inlet and outlet ports may be said to bedisposed, respectively, at the diagonally opposite upper and lower endportions of the bores in the casing. Air from the atmosphere is admitted-at 25 and conducted through a pipe 26, an admission valve 27 and a pipe28 to the lowpressure compressor 1. From the low-pressure compressor theair is conducted through a pipe 29 and an intermedi-ate cooler 30 to thepipe 10 and the highpressure compressor 2 as described hereinabove. Allpipes and coolers are disposed below the floor 32 of the machine roorn.

The compressor described hereinabove and illustrated on the accompanyingdrawings should be considered only as an example and the details of theinvention may be modified in several different ways within the scope ofthe claims` In order to unload the rotors from axial pressure the rotorsof the highand low-pressure stage may, for instance, be connected. Theinvention may, as stated in the preamble of this specification, also beemployed in screw motors which are driven by compressed air or hot gas.The invention may naturally be used in connection with twoormultiple-stage com pressors as well as in single-stage compressors.

What we claim is:

l. A rotary device of the character described for operation with anelastic uid working medium comprising a casing having two horizontallyextending intersecting bores and closure structure at the ends of saidbores and said casing further having a low pressure port and a highpressure port located, respectively, at the diagonally opposite upperand lower end portions of said bores, two screw-type rotors mounted forrotation in said bores and intermeshing to form working chambers forsaid working medium, which chambers register with different ones of saidports in different positions of rotation of the rotors and progressivelydecrease in length toward the highY pressure port as therotors revolve,said rotors having shafts located in a common horizontal plane in saidcasing, radial roller bearings mounted in said closure structure forsupporting said rotor shafts in said casing, a first passage for lowpressure working medium extending from a first opening on the undersideof said Y y casing to said low pressure port, and a second passage forhigh pressure working medium extending from said high pressure port to asecond opening on the underside of said casing.

2. A device as defined in claim l, in `which said first passagecomprises two branches extending respectively on opposite sides of themountings for said bearings to connect said first opening with said lowpressure port.

3. A rotary compressorplant of the character de scribed for compressingan elastic Huid Working medium comprising a oor structure, a foundationstructure, a compressor casing having two horizontally extendingintersecting bores and closure structure at the ends of said bores andsaid'oasing further 'having a low pressure inlet port and a highpressure outlet port located, respectively, at the diagonally oppositeupper and lower end portions of said bores, two screw-type rotorsmounted for rotation in said bores and intermeshing to form workingchambers for said working medium, which chambers register with differentones of said ports in different positions of rotation of said rotors andprogressively decrease in length toward the high pressure port as therotors revolve, said rotors having shafts located in a common horizontalplane in said casing, radial roller bearings mounted in said closurestructure for supporting said rotor shafts in said casing, a rst passagefor low pressure working medium extending from a rst opening on theunderside of the casing to sm'd low pressure inlet port, a secondpassage for high pressure working fluid extending from said highpressure port to a second opening on the underside of said casing, acooler mounted in said foundation structure, a fluid intake passage insaid foundation structure, a first conduit disposed substantially insaid foundation structure and leading from said intake passage to saidrst passage in the casing, a second conduit disposed substantially insaid foundation structure and leading to said cooler from said secondpassage in said casing, and means carried by said foundaton structureand Adisposed substantially above the level of said door structure fordriving said rotors.

References Cited in the file of this patent UNITED STATES PATENTS2,474,653 Boestad inne 28, 1949 2,727,364 Perez Dec. 20, 1955 FOREIGNPATENTS 384,355 Great Britain Dec. 8, 1932

